ipc,shm: move BUG_ON check into shm_lock

Upon every shm_lock call, we BUG_ON if an error was returned, indicating
racing either in idr or in shm_destroy.  Move this logic into the locking.

[akpm@linux-foundation.org: simplify code]
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/ipc/shm.c b/ipc/shm.c
index 6d76707..bd9c91f 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -155,8 +155,11 @@ static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id)
 {
        struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);
 
-       if (IS_ERR(ipcp))
-               return (struct shmid_kernel *)ipcp;
+       /*
+        * We raced in the idr lookup or with shm_destroy().  Either way, the
+        * ID is busted.
+        */
+       BUG_ON(IS_ERR(ipcp));
 
        return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
@@ -191,7 +194,6 @@ static void shm_open(struct vm_area_struct *vma)
        struct shmid_kernel *shp;
 
        shp = shm_lock(sfd->ns, sfd->id);
-       BUG_ON(IS_ERR(shp));
        shp->shm_atim = get_seconds();
        shp->shm_lprid = task_tgid_vnr(current);
        shp->shm_nattch++;
@@ -258,7 +260,6 @@ static void shm_close(struct vm_area_struct *vma)
        down_write(&shm_ids(ns).rwsem);
        /* remove from the list of attaches of the shm segment */
        shp = shm_lock(ns, sfd->id);
-       BUG_ON(IS_ERR(shp));
        shp->shm_lprid = task_tgid_vnr(current);
        shp->shm_dtim = get_seconds();
        shp->shm_nattch--;
@@ -1191,7 +1192,6 @@ out_fput:
 out_nattch:
        down_write(&shm_ids(ns).rwsem);
        shp = shm_lock(ns, shmid);
-       BUG_ON(IS_ERR(shp));
        shp->shm_nattch--;
        if (shm_may_destroy(ns, shp))
                shm_destroy(ns, shp);